1. Field of the Invention
The present invention relates to a zoom image-forming optical system and a microscope that includes the zoom image-forming optical system.
2. Description of the Related Art
As a variable power system for a zoom microscope that includes a zoom image-forming optical system having a variable focal length, a system that condenses a luminous flux from an objective lens by using a tube lens to form an intermediate image and that projects a magnified image of that intermediate image onto an image plane by using a relay lens with a zoom function is conventionally known. A zoom microscope adopting such a system is disclosed, for example, in Japanese Laid-open Patent Publication No. 09-274137.
A system that directly changes the magnification of an image formed on an image plane by using a relay lens with a zoom function, where an intermediate image is not formed, is also known. A zoom microscope adopting such a system is disclosed, for example, in Japanese Laid-open Patent Publication No. 2004-361778 and Japanese Laid-open Patent Publication No. 2006-154230.
The variable power system of a zoom microscope is generally classified into the above-mentioned two systems.